Tread for a unidirectional pneumatic tire

ABSTRACT

A tread for a unidirectional pneumatic tire has first, second and third circumferentially extending zones. The edges of the zones are parallel to the equatorial plane of the tire. The width of the first zone is between 25% and 50% of the tread width, the width of the second zone is between 15% and 35%, and the width of the third zone is between 25% and 50%. The first zone has substantially aligned lateral wide groove segments extending across the width of the first zone. The segments form an angle between 70 and 90 degrees with a plane in the first zone parallel to the equatorial plane. The second zone has substantially aligned lateral wide groove segments extending across the width of the second zone. The segments form an angle between 10 and 45 degrees with a plane in the second zone parallel to the equatorial plane. The third zone has substantially aligned lateral wide groove segments extending across the width of the third zone which are generally perpendicular to the lateral wide groove segments of the second zone. The segments form an angle between 45 and 70 degrees with a plane in the third zone parallel to the equatorial plane.

BACKGROUND OF THE INVENTION

1. Field of Invention

This invention relates generally to pneumatic tires and morespecifically to asymmetrical, directional tires.

2. Description of Related Art

In automotive vehicles, proper traction between the tire and the roadsurface is necessary for effective operation of the vehicle. Tires arerequired to provide good traction under a variety of different operatingconditions. For example, when the vehicle accelerates, the tire musttransfer the force to the road surface with a minimum of slippage toachieve maximum acceleration. Similarly, when the vehicle isdecelerating or braking, the tire must transmit this force to the roadwith a minimum of slippage to maintain controlled operation of thevehicle. When cornering, the tire is required to maintain good contactwith the road surface despite the weight of the vehicle shifting on itschassis and the presence of cornering forces. The presence of rain, snowor other friction-reducing substance on the road surface makes all ofthe above traction objectives more difficult to achieve.

Tire designers have sought to design tread patterns to improve tractionbetween the tire and the road surface. Some have been specificallydirected toward good traction under a variety of road surface conditionssuch as U.S. Pat. No. 4,545,415 to Lindner et al. and U.S. Pat. No.3,674,077 to Verdier. Both Lindner et al. and Verdier disclose tiretread designs featuring grooves which extend generally laterally acrossthe tire tread from tread edge to tread edge. Other tread designsfeature directional treads which are designed to rotate in one directiononly, such as U.S. Pat. No. 284,178 to Kawabata et al. and AustrianPatent No. 147,223. Still other tread designs seek traction advantagesthrough asymmetric tread designs such as U.S. Pat. No. Des. 223,599 toBusch et al.

While tire tread designers have met with some success, furtherimprovements are desirable in providing good traction under a variety ofoperating and road surface conditions.

SUMMARY OF THE INVENTION

The invention disclosed and claimed herein is a tread for aunidirectional pneumatic tire designed for use on paved road surfaces.The tread, when mounted on a casing, features first, second and thirdcircumferentially extending zones whose edges are parallel to theequatorial plane of the tire. The second zone is disposed between thefirst and third zone. The width of the first zone is between 25% and 50%of the tread width, the width of the second zone is between 15% and 35%of the tread width, and the width of the third zone is between 25% and50% of the tread width. The first zone has substantially aligned lateralwide groove segments extending across the width of the first zone. Thelateral wide groove segments, over a majority of their length in thefirst zone, form an angle between 70 degrees and 90 degrees with a planein the first zone which is parallel to the equatorial plane.

The second zone features substantially aligned lateral wide groovesegments extending across the width of the second zone. The lateral widegroove segments, over a majority of their length in the second zone,form an angle between 10 degrees and 45 degrees with a plane in thesecond zone parallel to the equatorial plane of the tire.

The third zone has substantially aligned lateral wide groove segmentsextending across the width of the third zone, generally perpendicular tothe lateral wide groove segments of the second zone.

The lateral wide grooves, of the third zone, over a majority of theirlength in the third zone, form an angle between 45 degrees and 65degrees with a plane in the third zone parallel to the equatorial plane.

BRIEF DESCRIPTION OF THE DRAWINGS

Other aspects of the invention will become apparent from the followingdescription when read in conjunction with the accompanying drawingswherein:

FIG. 1 is a plan view of a right tire with a tread according to thepresent invention with the normal, forward orientation being toward thetop of the page in the direction of the arrow;

FIG. 2 is a plan view of a left tire with a tread according to thepresent invention with the normal, forward orientation being toward thetop of the page in the direction of the arrow;

FIG. 3 is a plan view of a vehicle fitted with tire treads according tothe present invention mounted on the rear axle of the vehicle;

FIG. 4 is an enlarged plan view of a vehicle with tire treads tireaccording to the present invention mounted on the rear axle of thevehicle; and

FIG. 5 is a cross-sectional view of a tire with a tread according to thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

The invention also may be better understood in the context of thefollowing definitions, which are applicable to both the specificationand to the appended claims:

"Pneumatic tire" means a laminated mechanical device of generallytoroidal shape (usually an open-torus) having beads and a tread and madeof rubber, chemicals, fabric and steel or other materials. When mountedon the wheel of a motor vehicle, the tire through its tread providestraction and contains the fluid that sustains the vehicle load.

"Equatorial plane (EP)" means the plane perpendicular to the tire's axisof rotation and passing through the center of its tread.

"Dividing Plane (DP)" means the plane perpendicular to the tire's axisof rotation that divides a tire tread according to the present inventioninto zones.

"Tread" means a molded rubber component which, when bonded to a tirecasing, includes that portion of the tire that comes into contact withthe road when the tire is normally inflated and under normal load.

"Tread width" means the arc length of the tread surface in the axialdirection, that is, in a plane passing through the axis of rotation ofthe tire.

"Casing" means the carcass, belt structure, beads, sidewalls, and allother components of the tire excepting the tread and undertread. Thecasing may be new, unvulcanized rubber or previously vulcanized rubberto be fitted with a new tread.

"Groove" means an elongated void area in a tread that may extendcircumferentially or laterally about the tread in a straight, curved, orzig-zag manner. Circumferentially and laterally extending groovessometimes have common portions and may be subclassified as "wide","narrow", or "slot". A "slot" is a groove having a width in the rangefrom about 0.2% to 0.8% of the tread width, whereas a "narrow groove"has a width in the range from about 0.8% to 2% of the tread width and a"wide groove" has a width greater than 2% thereof. The "groove width" isequal to tread surface area occupied by a groove or groove portion, thewidth of which is in question, divided by the length of such groove orgroove portion; thus, the groove width is its average width over itslength. Grooves, as well as other voids, reduce the stiffness of thetread regions in which they are located. Slots often are used for thispurpose, as are laterally extending narrow or wide grooves. Grooves maybe of varying depths in a tire. The depth of a groove may vary aroundthe circumference of the tread, or the depth of one groove may beconstant but vary from the depth of another groove in the tire. If suchnarrow or wide grooves are of substantially reduced depth as compared towide circumferential grooves which they interconnect, they are regardedas forming "tie bars" tending to maintain a rib-like character in thetread region involved.

"Normal load" refers to the specific design inflation pressure and loadassigned by the appropriate standards organization for the servicecondition for the tire.

"Axial" and "axially" are used herein to refer to lines or directionsthat are parallel to the axis of rotation of the tire.

"Radial" and "radially" are used to mean directions radially toward oraway from the axis of rotation of the tire.

"Unit tread pressure" means the radial load borne per unit area (squarecentimeter or square inch) of the tread surface when that area is in thefootprint and the tire is loaded.

"Footprint" means the contact patch or area of contact of the tire treadwith a flat surface under normal load and pressure or under specifiedload, pressure and speed conditions.

"Net-to-gross ratio" means the ratio of the tire tread rubber that makescontact with the road surface while in the footprint, divided by thearea of the tread in the footprint, including non-contacting portionssuch as grooves.

In the drawings, the same numerals are used for the same components oritems in the several views. With particular reference now to FIGS. 1 and2, there is illustrated a tread 14, 15 according to the presentinvention which is mounted on a tire 14a, 15a. In a new tireapplication, the tread 14, 15 is attached to a tire casing which has notbeen vulcanized. The tire casing and tread are vulcanized together in amold, creating a new tire. In a retreading application, the tread can be"pre-cured", that is vulcanized prior to being bonded to the casingbeing retreaded. Alternatively, the tread pattern can be formed and thetread bonded to the casing in a single "mold-cure" retreading operation.For "pre-cured" retreading purposes, the tread may be in the form of ahoop or may be in the form of a flat slab which is then wrapped aroundthe circumference of the tire casing.

The tread 14, 15 is characterized by first, second and thirdcircumferentially extending zones 104, 106, 108. The zones are separatedby dividing planes DP1, DP2. The dividing planes are perpendicular tothe tire's axis of rotation and parallel to the tire's equatorial planeEP. The width of the first zone, is between 25% and 50% of the treadwidth. In the preferred embodiment, the width of the first zone is equalto 37.5% of the tread width. The width of the second zone is between 15%and 35%, and is preferably equal to 25% of the tread width. The width ofthe third zone is between 25% and 50% of the tread width and preferablyis equal to 37.5% of the tread width.

The first zone 104 is characterized by substantially aligned lateralwide groove segments 70 which extend across the width of the first zone.The lateral wide groove segments 70, over a majority of their length inthe first zone, form an angle between 70 degrees and 90 degrees with aplane in the first zone parallel to the equatorial plane EP. In thepreferred embodiment, the lateral wide groove segments form an angle of90 degrees with the plane in the first zone parallel to the equatorialplane.

The second zone 106 is also characterized by substantially alignedlateral wide groove segments 72 extending across the width of the secondzone. The lateral wide groove segments 72, over a majority of theirlength in the first zone, form an angle between 10 degrees and 45degrees with a plane in the second zone parallel to the equatorial planeEP. In the preferred embodiment, the lateral wide groove segments 72 ofthe second zone 106 form an angle of 23 degrees with a plane in thesecond zone parallel to the equatorial plane.

The third zone 108 is also characterized by substantially alignedlateral wide groove segments 74 extending across the width of the thirdzone which are generally perpendicular to the lateral wide grooves (72of the second zone 106). The lateral wide groove segments 74, over amajority of their length in the third zone, form an angle between 45degrees and 70 degrees with a plane in the third zone parallel to theequatorial plane EP. The angle of the lateral wide groove segments ofthe third zone are smaller than the angle of the lateral wide groovesegments of the first zone. In the preferred embodiment, the lateralwide groove segments 74 of the third zone 108 form an angle of 59degrees with a plane in the third zone parallel to the equatorial plane.

The lateral wide grooves 70 of the first zone 104 and the lateral widegrooves 74 of the third zone 108 merge into the lateral wide grooves 72of the second zone 106.

A tread 14, 15 according to the present invention is a directional,asymmetric tread design. The arrow shown in FIGS. 1 and 2 illustratesthe direction of the tire when in normal, forward use. As shown in FIG.3, preferably the tire will be mounted on the vehicle so that the firstzone 104 will be located between the second zone 106 and the vehicle.For example, the tread 14 shown in FIG. 1 is designed for use on theright side of the vehicle while the tread 15 shown in FIG. 2 is designedto be used on the left side of the vehicle.

This orientation makes best use of the intended functions of each zone.The first zone 104 is designed to provide longitudinal traction,especially during acceleration. The primary purpose of the third zone108 is to provide lateral traction for cornering and to prevent lateralsliding. The nearly perpendicular relationship between the grooves 72 ofthe second zone 106 and the grooves 74 of the third zone 108 is designedto inhibit lateral sliding of the tires 14a, 15a during turns whilecontinuing to provide good longitudinal traction for acceleration.

The net-to-gross ratio of each zone is at least 3% different than thenet-to-gross ratio of the other zones. The net-to-gross ratio of thefirst zone 104 is between 60% and 75% while the net-to-gross ratio ofthe second zone 106 is between 40% and 60% and the net-to-gross ratio ofthe third zone 108 is between 54% and 68%. Preferably, the net-to-grossratio of the first zone 104 is 67%, the net-to-gross ratio of the secondzone 106 is 50% and the net-to-gross ratio of the third zone is equal to61%. The net-to-gross ratio of each zone is at least 5% different thanthe other zones.

Net-to-gross ratios are important factors determining a tire's abilityto provide good traction under wet or slippery road conditions. Toadequately deal with wet road conditions in the footprint of a tire, atread design must either move standing water from the footprint throughgroove paths or absorb the water and hold it in the void areas of thetread, allowing the remaining areas of the tread to maintain goodcontact with the road surface. A low net-to-gross ratio improves atire's ability to absorb and hold water while in the footprint of thetire. However, a high net-to-gross ratio provides other performanceobjectives such as good tread wear and stability. Generally speaking,the higher the tread unit pressure, the greater the ability for thetread to squeeze water out of the footprint and provide good contact.Therefore, points of low unit tread pressure require a lowernet-to-gross ratio to provide good traction. For the reasons statedabove, in the preferred embodiment of a tread according to the presentinvention, the center of pressure is located in the first zone, whichhas the higher net-to-gross ratio.

In the preferred embodiment, the treads 14, 15 are mounted on the rearaxle of a vehicle as shown in FIGS. 3 and 4. In this embodiment, thetreads 14, 15 are wider than the treads used on the front tires. Thisdifference in the widths of the front and rear tires causes thenet-to-gross ratio differences among the zones to be more important.Because the spray 62 from the front tire can partially fill the grooves72, 74, 77, 78 of the second and third zones 106, 108 before thatportion of the tread 14, 15 can even enter the footprint, thenet-to-gross ratio of the second and third zones, 106, 108 must be lowerthan that of the first zone 104. The lower net-to-gross ratios of thesecond and third zones enables them to accommodate the additional waterdue to the front tire. In the preferred embodiment, the front tire is 10inches wide and the rear tire is 16 inches wide. The first zone 104 is 6inches wide, the second zone is 4 inches wide and the third zone 108 is6 inches wide.

The lateral wide groove segments 70 of the first zone 104 areintersected by other wide groove segments 76. The other wide groovesegments 76 form an angle between 10 degrees and 45 degrees with a planein the first zone which is parallel to the equatorial plane of the tire.In the preferred embodiment, the other wide groove segments 76 form anangle of 20 degrees with the plane in the first zone which is parallelto the equatorial plane.

The lateral wide groove segments 72 of the second zone 106 are alsointersected by other wide groove segments 77. These wide groove segments77 form an angle between 0 degrees and 10 degrees with a plane in thesecond zone which is parallel to the equatorial plane. In the preferredembodiment, these wide groove segments 77 form an angle of 0 degreeswith a plane in the second zone parallel to the equatorial plane.

The lateral wide groove segments 74 of the third zone 108 areintersected by other wide groove segments 78. These other wide groovesegments 78 form an angle between 10 degrees and 35 degrees with a planein the third zone that is parallel to the equatorial plane. In thepreferred embodiment, these wide groove segments 78 form an angle of 22degrees with a plane in the third zone parallel to the equatorial plane.

The intersection of the lateral wide groove segments 70 of the firstzone 104, the lateral wide groove segments 72 of the second zone 106,and the lateral wide groove segments 74 of the third zone 108 by theother wide groove segments 76, 77, 78 form blocks 50. The blocks in thefirst zone are generally in the shape of a trapezoid. The blocks in thesecond and third zones are generally in the form of a parallelogram. Theleading edge 52 of a block 50 contacts the road surface prior to thetrailing edge 54 of the block when the tire is rotating in its forwarddirection. The leading edge 52 of the blocks 50 in the first zone 104 iswider than the trailing edge 54 of the blocks 50 in the first zone. Thewider leading edge is designed to provide improved traction forlongitudinal acceleration.

With reference to FIG. 5, the radially outermost surface 90 of the block50 is convexly curved in the radially outward direction. In thepreferred embodiment, this curvature in the axial direction only; thecircumferential direction has no curvature apart from the usualcurvature associated with a round tire. The curvature of the surface ofthe element helps move water from the center of the block to the treadgroove. The curvature shown in FIG. 5 is exaggerated for clarity. In thepreferred embodiment, the actual radius of curvature for the blocksurface is about 4 inches

With reference to FIGS. 1 and 2, the blocks 50 in the first and thirdzones 104, 108 have slots 55. The slots provide paths for water to movefrom beneath the block to the groove.

Based on the foregoing description of the invention, what is claimed is:
 1. A tread for unidirectional pneumatic tire, the tire being for use on paved road surfaces, the tread, when mounted on a casing, comprising:first, second and third circumferentially extending zones, the edges of the zones being parallel to the equatorial plane of the tire, the second zone being disposed between and contiguous with the first and third zone; the width of the first zone being between 25% and 50% of the tread width, the width of the second zone being between 15% and 35% of the tread width, the width of the third zone being between 25% and 50% of the tread width; the first zone having substantially aligned lateral wide groove segments extending across the width of the first zone, the lateral wide groove segments, over a majority of their length in the first zone, forming an angle between 70 degrees and 90 degrees with a plane in the first zone parallel to the equatorial plane, the second zone having substantially aligned lateral wide groove segments extending across the width of the second zone, the lateral wide groove segments, over a majority of their length in the first zone, forming an angle between 10 degrees and 45 degrees with a plane in the second zone parallel to the equatorial plane; and the third zone having substantially aligned lateral wide groove segments extending across the width of the third zone which are generally perpendicular to the lateral wide groove segments of the second zone, the lateral wide groove segments of the third zone, over a majority of their length in the third zone, forming an angle between 45 degrees and 70 degrees with a plane in the third zone parallel to the equatorial plane, provided that the angle of the lateral wide groove segments of the third zone are smaller than the angle of the lateral wide groove segments of the first zone.
 2. A tread as in claim 1 wherein the tread has wide grooves which intersect lateral wide grooves to form blocks, the blocks having a leading edge and a trailing edge, the leading edge of the blocks contacting the road surface prior to the trailing edge of the blocks when the tire is rotating in its forward direction, the leading edge of the blocks in the first zone being wider than the trailing edge of such blocks.
 3. A tread as in claim 2 wherein the tread has a pattern of tread elements with a corresponding net-to-gross ratio, the net-to-gross ratio of each zone being at least 3% different than the other zones.
 4. A tread as in claim 3 wherein the net-to-gross ratio of each zone is at least 5% different than the other zones.
 5. A tread as in claim 1 wherein the net-to-gross ratio of the first zone is between 60% and 75%.
 6. A tread as in claim 5 wherein the net-to-gross ratio of the first zone is between 60% and 70%.
 7. A tread as in claim 6 wherein the net-to-gross ratio of the third zone is between 54% and 68%.
 8. A tread as in claim 7 wherein the tread has a center of pressure, the center of pressure being disposed in the first zone.
 9. A tread as in claim 1 wherein the width of the first zone is between 3 and 9 inches, the width of the second zone is between 1 and 6 inches, and the width of the third zone is between 3 and 9 inches.
 10. A tread as in claim 1 wherein the lateral wide grooves of the first zone merge into the lateral wide grooves of the second zone.
 11. A tread as in claim 10 wherein the lateral wide grooves of the third zone merge into the lateral wide grooves of the second zone.
 12. A tread as in claim 2 wherein at least one block has the shape of a trapezoid. 